The present invention relates to a method and apparatus for applying a liquid to a substrate and, more particularly, to an automated method and apparatus for applying one or more liquids, including for example a primer coating or a treatment liquid, to a glass panel, such as a window assembly.
The recent trend in vehicles is to produce an aerodynamically shaped vehicle with larger windows to improve visibility. In order to reduce the aerodynamic drag and enhance the overall appearance, window assemblies are more recently mounted to the vehicle body by an adhesive, often in combination with one or more fasteners which are mounted to an inner surface of the window panel or are embedded in a gasket which has been previously extruded or molded on to the window panel after priming of the substrate surface. It has been found that the priming of the substrate surface improves the adhesion of the gasket to the substrate. The adhesive is applied to the surface of the panel or the gasket, for example by extrusion. To install, the window assembly is then pressed against the mounting flange or decking of the vehicle body to which the adhesive adheres after curing. In other windows, the securement of the window panel to the vehicle is achieved by a fastening system. In some fastening systems, the fastener is adhered directly to the surface of the window by an adhesive. Before applying such adhesives, the window panel is preferably treated with a treatment liquid, such as an acid solution or cleaning solution, to prepare the glass panel and improve the adhesion of the adhesive to the glass panel. In many windows, therefore, the adhesive often provides the primary attachment of the panel to the vehicle.
However, window assemblies often include compound curvatures, which make it hard to automate the application of the gasket primer or treatment liquid. In preferred forms, the primer or treatment liquid is directly applied to the window substrate rather than sprayed or wiped on in order to achieve a more uniform coverage and thickness. As a result of the compound curvatures and the irregularities in the surface topology of window panels, direct application of a primer or treatment liquid to a window assembly has been more typically accomplished manually with the use of an applicator.
Conventional applicators include a tip, for example a pad, including a felt pad, and a reservoir which holds a supply of the primer solution or treatment liquid. However, when applying a liquid that dries when exposed to air, such as most conventional primers, the pads of the applicators must be replaced frequently. For example, primers dry relatively quickly in ambient conditions and tend to harden the pad and clog up the applicator. As a result, applicator tips or pads require frequent replacement, and the applicator reservoir must be cleaned and flushed before refilling.
As described above, heretofore, manual application of the primer has been preferred due to the compound curvatures and irregularities in the surface topology of the window assembly substrate and more consistent results due to varying conditions of the substrate (i.e. frit, contamination, temperature, or the like). Furthermore, it has been found that in order to achieve optimal results, the liquid is preferably applied with a constant pressure so that a uniform coating can be achieved. Heretofore, this constant pressure has been easier to achieve with manual application. However, manual application may result in inaccurate primer or treatment liquid placement and the coating thickness may vary with each worker. Moreover, conventional primer systems are open systems which result in prolonged exposure of the primer to contaminants. Given the reactive nature of primer solutions, these open systems cause the primer solution to prematurely cure. Therefore, these open primer systems are wasteful and require frequent cleaning and or replacement of the applicators.
Consequently, there is a need for a liquid application system which will produce the same advantages of a manually applied coating system, including a substrate surface and substrate condition variation sensitive system, but will require less material usage and, consequently, produce less waste than a manual application process. Furthermore, there is a need for a liquid application system that will provide a longer life for the applicator tip. In addition, there is a need for a primer application system which can provide a highly accurate primer or treatment liquid placement and produce a repeatable coating thickness. Moreover, there is a need for a closed primer system which will reduce waste and increase the life of the applicator and further reduce contamination of the treatment liquid or primer solution.